1. Field of the Invention
The present invention relates to a technique for adjusting a position of a detection area and detecting a positional deviation, in a range finder incorporated into a vehicle by which a distance to an object to be detected such as a preceding vehicle is measured by utilizing waves such as laser beams.
2. Description of the Related Art
Conventionally, they have extensively developed radar to be incorporated into a vehicle for monitoring an obstacle located ahead and for controlling running in chase of a preceding vehicle. Concerning the system of the radar, an electric wave system and a laser beam system are well known. In the above systems, waves of electric waves or laser beams are sent to an object to be detected located in a predetermined area, and a distance from the vehicle to the object to be detected can be found by a propagation delay time between a time at which a signal of the waves has been emitted and a time at which a reflecting signal of the waves has been received.
For example, in the case of a range finder of the laser beam system, that is, in the case of a so-called laser radar, the propagation delay time is measured as follows. While scanning is being conducted on a predetermined scanning area, the laser beams are irradiated thereon. In order to find the propagation delay time between the emitted laser beams and the reflected laser beams, light emitting timing is made by a control circuit, and a counter starts in accordance with the light emitting timing. Simultaneously, a laser diode (hereinafter referred to as "LD") is driven by a laser diode drive circuit, so that the laser beams can be emitted. The laser beams reflect on the object to be detected and return to the range finder. The laser beams thus returned are received by a photo diode (hereinafter referred to as "PD"). In the case where reflected laser beams, the intensity of which is higher than a light reception threshold level, are obtained, the timing is taken into a control circuit, and the counter stops, so that the propagation delay time can be measured.
On the other hand, a direction in which the object to be detected is located is judged according to a scanning angle at the laser beam emitting timing or the reflected laser beam receiving timing.
According to distance data thus measured from the range finder to the object to be detected, direction data, the data of received light and vehicle speed data obtained by a vehicle speed sensor, the individual pieces of the distance data are grouped and made to correspond to the previous data, so that a relative speed to the object to be detected is calculated. Then it is judged what is the object, for example, it is judged whether the object is a car, a bike, a man, a billboard, or a reflector located on a roadside, and an object to be followed is specified and an object to be warned is specified.
In the range finder of this type, in the case where the range finder is actually attached to the vehicle, when an actual detecting area deviates from an ideal detecting area to detect the object to be detected such as the preceding vehicle, that is, when an angle region, in which reflected waves are received and the above measurement is conducted, deviates from an angle region, which extends in front of the vehicle in the transverse direction, reliability of the measurement result is deteriorated in accordance with the deviation. Accordingly, in order to keep a condition in which the above deviation is not caused, it is necessary to conduct axis adjustment, which is referred to as an optical axis adjustment work in the case of a laser radar, in which a center of the detection area is adjusted, on a production line of vehicles or in a garage at the time of inspection of vehicles.
As conventional methods of adjusting a position of the detection area, which will be also referred to as "axis adjustment" hereinafter, there is provided a method in which a level is used to adjust an attaching angle of a detection head of the range finder, that is, to adjust an angle in the vertical direction.
Also, there is another method in which the range finder is incorporated into the vehicle which is in a stopped state, a reference target, which is a reference reflecting body prepared specially, is disposed at the center of an ideal detecting area, and an excellent environment having no disturbance in which any objects except for the reference target are not detected is prepared, and then the range finder is actually operated, and for example, the attaching angle of the detection head of the range finder and a parameter of the inside are changed so that position data of the reference target to be detected can coincide with the center of the detection area.
However, the following problems may be encountered in the above conventional axis adjusting techniques.
(1) In the method in which the level is used for adjusting the axis, it is impossible to conduct adjustment in the transverse direction.
(2) In the method in which the specially prepared reference target is disposed at an appropriate position and the axis adjustment is conducted, it is necessary for a worker to have a pretty high skill for adjustment, and further it takes very long time for adjustment. That is, in order to position the reference target at an ideal position with high accuracy, it is necessary to prepare a special jig and further high skill is required. Further, it is necessary to readout position data of the reference target, and also it is necessary to change the attaching angle of the detection head and the parameter of the inside so that the position data of the reference target can coincide with the center of the detection area. For the above reasons, it is necessary for a worker to receive a pretty high education and to have the pretty high skill.
(3) Further, the above method in which the reference target is used is disadvantageous as follows. According to the above method, the vehicle stops, and adjustment is conducted under the condition that the reference target is disposed on the central axis of a body of the vehicle. Therefore, a difference between the actual advancing direction of the vehicle and the above central axis surely becomes an error, and accuracy is deteriorated due to the above error.
That is, the body of the vehicle is not necessarily directed to the advancing direction. Although it is impossible for a man to recognize such the difference, a minute angle accuracy of several milliradian is required for this type range finder. Therefore, the above difference causes a problem.
(4) Further, by using only the conventional adjusting techniques, it is difficult to keep the center of the detecting area at the appropriate position. That is, when the range finder is in a stationary condition, for example, when the range finder is shipped from a factory, it is kept in the stationary condition. At this time, it is possible to adjust the axis of the range finder with accuracy. However, after the shipment from the factory, it is conveyed over a long period of time and some shocks are given to the range finder. For the above reasons, there is a possibility that the detecting area deviates, that is, there is a possibility that the axis of the range finder deviates from a predetermined position. In this case, unless the axis adjustment is conducted again in a periodical checkup, the range finder continues to be used while the detecting area is deviated from the appropriate position. For the above reasons, there is a demand of developing a detection technique by which deviation of the optical axis can be easily detected.
In this connection, in Japanese Patent Application No. Hei 8-114483, the present applicant has proposed a technique by which the above axis adjustment can be automatically conducted while the vehicle is running. This technique is summarized as follows. While the vehicle is running, it is automatically recognized whether or not detection data of the preceding vehicle can be used as a reference of the axis adjustment. When it is recognized that the detection data can be used as the reference of the axis adjustment, the inside parameter (set position data of the detection area) is automatically changed by the control processing function in accordance with the detection data of the preceding vehicle.
According to the above technique, it is possible to conduct the axis adjustment without using the special jig or skill, and further the axis adjustment is not affected by a factor of disturbance, that is, the axis adjustment can be automatically conducted while an user is not aware of it. However, even if the above technique is applied, it takes long time to conduct the axis adjustment. Accordingly, there is a demand of reducing the axis adjustment time.
The reason why the long time is required for conducting the axis adjustment is described as follows. The detection data of common preceding vehicles are not constant, for example, even when the preceding vehicle is running on a straight road, the detection data somewhat changes. Further, it is difficult to precisely judge that both the preceding vehicle and the self-vehicle are running on the straight road stably, and it is difficult to obtain correct data. Therefore, in order to conduct the adjustment with high accuracy, it is necessary to collect a large number of pieces of detection data of the preceding vehicle over a pretty long period of time, for example, for about two hours, so that an average can be used as reference data (the most appropriate position of the center of the detection area).
For the above reasons, the technique disclosed in the aforementioned Japanese Patent Application is disadvantageous in that it is not preferable to use the technique as the method of adjusting the axis at the shipment from the factory or at the time of periodical checkup. The reason is that the axis adjustment requires the long time, which causes an increase in personnel expenses, that is, the manufacturing cost and the maintenance cost are increased. Therefore, it is desired to provide an adjusting method and an apparatus for the adjustment which can be used by a skilled worker in the case of shipment from the factory or in the case of periodical maintenance.
When there is a large deviation of the axis in the transverse direction which can not be adjusted by changing the inside parameter, or when there is the deviation of the axis in the vertical direction, it is impossible for the technique disclosed in the above Japanese Patent Application to meet the requirement. Therefore, it is desired to provide a technique by which the aforementioned deviation of the axis can be automatically detected.